In an electrostatographic process, a system is used whereby a uniform electrostatic charge is placed upon a reusable photoconductive surface. The charged photoconductive surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original on the photoreceptor. The latent image is developed by depositing finely divided marking and charged particles (toner) upon the photoreceptor surface. The charged toner is electrostatically attached to the latent electrostatic image areas to create a visible replica of the original. The toned developed image is then transferred from the photoconductor surface to a final image support material, such as paper, and the toner image is fixed thereto by heat and pressure to form a permanent copy corresponding to the original.
In Xerographic systems of this type, a photoreceptor surface is generally arranged in a drum or belt configuration to move in an endless path through the various processing stations of the Xerographic process. The photoconductive or photoreceptor surface is generally reusable whereby the toner image is transferred to the final support material, and the surface of the photoreceptor is prepared to be used once again for another reproduction of an original. In this endless path, several stations of corona charging are traversed. These charging stations may involve one or a cluster of chargers including dicorotron or other corotron units.
Several methods and devices are known for applying an electrostatic charge to the photosensitive member such as the use of electron-emitting pins, an electron-emitting grid, single corona-charging structures and single or multiple dicorotron wire assemblies. These will be referred to as “chargers” throughout this disclosure and claims. In recent development of multifunctional Xerographic machines where copiers can provide several functions, the need for several reliable chargers or charging assemblies exists in order to assure that high quality final copies are produced.
Usually, in electrostatographic or electrostatic copy processes, as those above noted, a number of chargers such as corotrons, scorotrons, or dicorotrons are used at several various stations around the photoreceptor. For example, the chargers are used at the station that places a uniform charge on the photoreceptor, at a transfer station, at a cleaning station, etc. In today's high speed copiers, it is important that all corotrons (or chargers) are controlled for efficient and uniform charging. Generally, one structure of a dicorotron charger uses a thin, glass-coated wire mounted in an elongated U-shaped housing between two insulating anchors called “insulators”. These support the wire in the U-shaped housing in a spring-tensioned manner in a singular plane. This dicorotron unit or assembly, as above noted where aluminum usually comprises the housing, is in one embodiment an elongated U-shaped shield. The wire or corona-generating electrode is typically a highly conductive, elongated wire situated in close proximity to the photoconductive surface to be charged.
As earlier noted, the charging of the photoreceptor or other surfaces is necessary for the proper reliable operation of the Xerographic machine.
Charging devices historically come in several forms including wires, pins, grids, and the like and are generally referred to as corotrons, scorotrons and dicorotrons; all will be referred to in this disclosure as “chargers” or a source of “corona” discharge. These charging devices typically use high voltages to create a corona which contains electrons and/or ions for deposit on a surface.
Non-uniform charging caused by dirty wires or an otherwise faulty charger cause the appearance of a printed copy to appear blurry or have areas where the image is entirely missing (deleted). Corrective means and specifically automated and continuous corrective means for countermining the effects of dirty chargers, faulty chargers, or improperly installed chargers are seriously needed.
With the advent of high speed xerography reproduction machines wherein printers can produce at a rate in excess of three thousand copies per hour, the need for corotrons or dicorotrons at many processing stations is needed in a reliable and dependable manner in order to utilize the full capabilities of the reproduction machine. These corotron systems must operate flawlessly to virtually eliminate unacceptable print quality and machine shutdowns due to corotron malfunctions.
Generally, in electrostatographic or electrostatic printing processes, a number of corotrons or dicorotrons are used at various stations around the photoreceptor. For example, the dicorotrons are used at the station that places an initial uniform charge on the photoreceptor, at a transfer station to control the charge on the backside of the media receiving the toned image, at a cleaning station where reduction of the intensity of the electrostatic forces between the photoreceptor and toner is required and at a plurality of other related processes. In today's high speed printers, it is important that all corotrons (or dicorotrons) are in perfect working order since one corotron malfunction can easily render the entire printing process useless. Some high speed printers including color printers use several dicorotron units. In one embodiment, as many as sixteen corotron or dicorotron units are used. So, maintaining each corotron or dicorotron unit in perfect working order is essential to the proper functioning of these complex fast color printers. It is common to use one or several corona-generating device(s) (“corotron” or “dicorotron”) for depositing the electrostatic at the above-noted stations. Generally, the structure of a dicorotron uses a thin, glass-coated wire mounted between two insulating anchors or end blocks called “anchors” which support the wire in a highly tensioned manner in a singular plane. In this disclosure, the term “anchors” includes insulator, end blocks, insulating anchors, etc. These anchors are installed between flexible holders or clamps or anchor inserts that maintain the anchors in place. These anchor inserts are fixed at two opposite ends of a U-shaped dicorotron “housing” or “shells” or “shield”. The wire or corona-generating electrode is typically a highly conductive elongated wire situated in close proximity to the photoconductive surface to be charged. Often, the corona discharge electrode is coated with a dielectric material such as glass, for glass coating improves charging uniformity throughout the electrode's life. Since the wire electrode is comprised of a thin outer glass brittle coating, it may be easily damaged or dirtied, or contaminated as earlier noted. In some instances even very gentile handling or cleaning of this electrode often results in fracture of the glass coating which could cut or injure the user, cause damage to surrounding parts, or cause contamination to the printer itself. While cleaning sometimes corrects problems in this corona electrode, it is sometimes necessary to replace the wire due to degradation in the corona performance or even in breakage of the electrode which could occur during the cleaning.
If the flaws in the charger are determined by a suitable sensing device such as a field probe, particularly a high resolution field probe and subsequent corrections are made to the output by a suitable controller before the final copy or print is made, a high advance in electrostatic marking systems will be accomplished. Since the output from a charger can vary across the length, width, and area of the charging element, precise control of the output over vary small, local areas of the charger to achieve a uniform output across the entire area of the charger device is needed. Irregularities or non-uniformities in the local output of a charger over a width of as little as a few micron or less, or over an area of about 10 square microns, or less can cause flaws within and thereby adversely impact upon the quality of a xerographic print. Controllers of the type integral close feedback loop controllers, or proportional, or a proper combination of them, can process the sensed charge surface and provide actionable information sequentially distributed to various actuators. The actuators considered include controlling the output of the charge device, which, depending on the type of charge device, can be accomplished by changing the voltage input to each of the charging elements of the charge device. Considered distributed controller schemes include multiobjective distributed controllers using other actuators to compensate for the flaws in the charger, like modulating pixel to pixel the laser exposure in order to compensate for the charge variability across the charged photoreceptor surface, or by replacing the faulted charging device. In a process color reprographic machine, for example a CMYK printer, the controller scheme described above is repeated for each color. But this concept is extended to other xerographic base machines, for example, machines printing black and one or more highlight colors, five or more process color machines, and so on. By the term “flaws in a charger” is meant non uniform charging or contaminated or dirty wires or faulty corotron (charger) installation which would result in perturbation, including a microscopic perturbation or disturbance, in the output corona or ion stream. By the term “flaws in a print” is meant any undesired, non-uniform appearing region in the printed image, any void region within the printed image or otherwise unacceptable defect such as a jagged line that is visible or otherwise detected by the end-user.